Somerville K-8 Schools and Students

This is a project by Carole Turley Voulgaris. The associated GitHub repository is here. Feel free to submit an issue with questions or comments.

Where do school children in Somerville live?

Here is map showing the approximate spatial distribution of Somerville children enrolled in school (kindergarten through 8th grade) based on data from the 2021 5-year sample of the American Community Survey (see this technical appendix for details). Each dot represents one student. Dots are colored to differentiate between children in households with incomes above the poverty level and those in households below the poverty level.

Spatial distribution and poverty status of K-8 students in Somerville. Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Spatial distribution and poverty status of K-8 students in Somerville. Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

This next map is similar, with each dot representing one student and dot colors indicating whether the child is non-Hispanic and white or either non-white or Hispanic1.

Spatial distribution of K-8 students in Somerville, based on block-group-level data from the American Community Survey (2020 5-year sample). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Spatial distribution of K-8 students in Somerville, based on block-group-level data from the American Community Survey (2020 5-year sample). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Where is the middle of Somerville?

One way to think about the middle of a shape (for example, the boundary of a city like Somerville) is its centroid. If you cut out a piece of cardboard in the shape of Somerville, and you wanted to balance your Somerville-shaped cardboard on the point of a pencil, the centroid is where you’d need to put the pencil in order for it to balance and stay level.

The population-weighted centroid is another useful way to think about the middle of a geographic area. If you had that same piece of cardboard, and you could stick a bunch of heavy pins to the top of it, with each pin at a student’s home address, and then you tried to balance it on the tip of a pencil, it would fall off your pencil if you placed it at the centroid you were using before. The population-weighted centroid is where you would have to put the pin to balance your little Somerville cardboard now that it’s been weighted to reflect the population of students. Another term for a population-weighted centroid is the center of population.

When we’re thinking about where schools are needed, the center of the student population is probably more relevant than the simple geometric centroid, since land doesn’t go to school; children do.

Here is a map showing Somerville’s center of the K-8 student population.

Population-weighted centroid of K-8 students in Somerville. Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Population-weighted centroid of K-8 students in Somerville. Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Average distances to school

Since Winter Hill Community Innovation School is so centrally-located, it plays an important role in minimizing the average distance between a Somerville student’s home and the nearest school.

Here is a map showing the walking distances2 to the nearest K-8 school3 for K-8 students in Somerville.4

Distances to the nearest school for K-8 students in Somerville (existing school locations). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Distances to the nearest school for K-8 students in Somerville (existing school locations). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Here is a map showing the same analysis under a hypothetical condition where the Winter Hill building is removed from the set of schools without being replaced.

Distances to the nearest school for K-8 students in Somerville (without WHCIS). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Distances to the nearest school for K-8 students in Somerville (without WHCIS). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Here is the same map for a hypothetical condition where the Winter Hill building is replaced by a building at 8 Bonair Street.

Distances to the nearest school for K-8 students in Somerville (WHCIS moved to 8 Bonair Street). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Distances to the nearest school for K-8 students in Somerville (WHCIS moved to 8 Bonair Street). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Here is the same map for a hypothetical condition where the Winter Hill building is replaced by a building at 554 Broadway.

Distances to the nearest school for K-8 students in Somerville (WHCIS moved to 554 Broadway). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Distances to the nearest school for K-8 students in Somerville (WHCIS moved to 554 Broadway). Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Obviously, the students for whom the distance to the closest school would change the most with the removal or relocation of WHCIS would be those for who the location at 115 Sycamore Street would have otherwise been the closest school (shown in the map below).

Locations of students for whom 115 Sycamore Street is the closest school. Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Locations of students for whom 115 Sycamore Street is the closest school. Cartolight basemap based on data from Open Street Map (c) OpenStreetMap contributors.

Here is a table showing the average walk time to the closest school for K-8 students under each of the above scenarios. The first column shows average walk times to the closest school for all students in Somerville. The second column shows average walk times to the closest school for those students for whom the school at 115 Sycamore Street is currently the closest school.

Scenario Average walking time to the closest school (all students) (minutes) Average walking time to the closest school (students closest to 115 Sycamore St) (minutes)
WHCIS at 115 Sycamore Street 11.0 11.5
WHCIS removed without replacement 12.6 18.2
WHCIS replaced with school at 8 Bonair Street 12.1 17.9
WHCIC replaced with a school at 554 Broadway 12.3 17.2

  1. The American Community Survey records race (white, Black, Asian, etc) and ethnicity (either Hispanic or non-Hispanic) separately.↩︎

  2. This is the distance students would need to walk using the existing street network, which is different from the straight-line “as the crow flies” distance. Distances are calculated using the r5r package in R.↩︎

  3. Brown school is included, even though it only serves grades K-5; Capuano is not included, even though it serves Kindergarten and first grade↩︎

  4. Refer to the technical appendix for details on how the residential locations of students are approximated.↩︎